Permanent or long term hair removal for cosmetic reasons has been accomplished by various methods. For example, hair can be removed by heating the hair and the hair follicle to a high enough temperature that results in coagulation. It is known that blood is coagulated when heated to temperatures on the order of 50-70.degree. C. Heating of the epidermis, the hair and the hair follicle to temperatures on the same order of magnitude will cause coagulation in the epidermis as well as the hair follicle and will result in permanent or long term removal of the hair with the unwanted result of scarring.
One common method of hair removal without scarring, often called electrolysis, is based on the use of "electric needles" that applies electric current to each hair through the needle. The current heats the hair and not the epidermis, causes its carbonization and also causes coagulation of the tissue adjacent to the hair as well as some coagulation of the micro-vessels that feed the hair follicle. While the electric needle method can remove hair permanently or long term without scarring, its use is practically limited because the treatment is painful and the procedure is generally tedious and lengthy.
Light can also be used effectively to remove hair. For example, prior art methods of hair removal involve the application of pulsed light. R. A. Harte, et al., in U.S. Pat. No. 3,693,623, and C. Block, in U.S. Pat. No. 3,834,391, teach hair removal by coagulating individual hairs with a light coupled to the individual hair by an optical fiber at the immediate vicinity of the hair. Similarly, R. G. Meyer, in U.S. Pat. No. 3,538,919, removes hair on a hair by hair basis using energy from a pulsed laser. A similar invention using small fibers is described in U.S. Pat. No. 4,617,926 to A. Sutton.
A wide variety of lasers have been used in dermatological applications for treatment of such conditions as vascular lesions (e.g. hemangiomas), pigmented lesions (e.g., nevi), tattoo removal, lentigines, cafe-au-lait macules, and other skin conditions and lesions. Through the principles of selective photothermolysis, specific wavelengths of light are known to be absorbed to a greater or lesser degree in certain skin pigments, tattoo inks, heme (blood pigment) or other chromophores. Wavelength selection also allows the targeting of these pigments and related structures at various depths within the dermis based on the magnitude of total absorption and light scattering as a function of depth.
Selective coagulation by wavelength absorption requires that the light energy used has a wavelength that is preferentially absorbed by the target structure or tissue. It also requires that a high enough power be used to cause tissue damage and that the heat be absorbed in the target structures faster than it is dissipated to surrounding tissue.
U.S. Pat. No. 4,388,924 to H. Weissman, et al. discloses a system wherein a narrow, focused beam of light is aimed at the epidermis adjacent to the hair such that an extension of the beam intersects the hair root at an angle relative to the skin's surface. A pulse, disclosed as a short pulse of less than 400 milliseconds but more than 10 milliseconds, passes through the skin and is selectively absorbed in the hair root destroying its blood supply.
The Weissman patent discloses apparatus which employs a manually controlled two-axis positioning system supporting the focusing system that is connected to a laser light source, preferably argon, by a flexible fiber optic bundle. The argon beam has most of its energy in the wavelength range of 482-520 nanometers. The Weissman patent further discloses that light of that wavelength passes through relatively light human skin without any appreciable absorption yet is highly absorbed in a dark hair root. Thus, the Weissman patent discloses selective coagulation by light absorption as a function of wavelength. The thermal energy produced upon absorption of the light energy within the hair root causes coagulation of the blood vessels and destroys the hair root. The hair body is generally vaporized in the process. Finally, Weissman claims that the process is relatively painless to the patient because of the low degree of absorbency and short pulse within the dermis.
The above prior art techniques suffer from a number of limitations. First, techniques for irradiating an individual hair follicle are time consuming and, therefore, not generally practical for removing hairs other than from a very small region or from a region having few hairs situated therein. The procedure can also be painful, particularly if a needle-like element is inserted in the hair follicle to facilitate light energy reaching the bulge and the root or papilla, which are the parts of the hair follicle which must be destroyed in order to prevent regrowth of the hair. Furthermore, it is difficult to get sufficient energy at the wavelength described to the required portions of the follicle to cause destruction thereof without also causing significant damage to the surrounding tissue and, thus, causing pain and injury to the patient.
Using the principles of selective coagulation by wavelength absorption or photothermolysis, certain laser wavelengths at short pulse durations (several picoseconds through several milliseconds) have been shown to have therapeutic benefits for specific types of lesions or treatments. For example, the flash-lamp-pumped, pulsed dye laser radiation at 585 nm is selectively absorbed by hemoglobin in capillary beds and small blood vessels and is used to treat vascular lesions such as hemangiomas. While shorter wavelengths (e.g., 532 nm) are also selectively absorbed by blood and can be used, they do not penetrate as deeply in the lesion as the 580-590 nm units and are sometimes less effective in thicker lesions. The Q-switched ruby (694 nm), alexandrite (755 nm) and neodymium: YAG (1064 nm) lasers have increasingly longer wavelengths, are deeper-penetrating and are absorbed preferentially by melanin rather than hemoglobin. These pulsed lasers are therefore used to treat pigmented lesions (e.g., nevus of Oti) and tattoo inks of dark colors. The CO.sub.2 laser, in contrast to the above lasers, is absorbed by the water content in tissue and is therefore non-selective by colors. One example of CO.sub.2 laser use in dermatology is for superficial skin vaporization (cosmetic skin resurfacing) using a high-energy, short-pulsed output or a scanned continuous-output laser beam.
High-power diode lasers can now produce radiation at wavelengths of 650-700 nm, 730-1000 nm and 1880-1960 nm. Diodes are available in a wide choice of wavelengths and are efficient converters of electrical energy to light. Some diode laser outputs can be pulsed (e.g., picosecond to nanosecond) like the above solid state lasers but they cannot practically produce the very high peak power (e.g., 20-1,000 kilowatts) needed to achieve selective coagulation by wavelength absorption without unwanted tissue injury.
Treatment of pigmented skin lesions based on selective coagulation by wavelength absorption or photothermolysis has been performed using the Q-switched ruby laser, the Q-switched Nd: YAG laser and the Q-switched alexandrite laser. With these lasers, a high peak power output with a very short duration selectively vaporizes melanin-containing cells. That is, the melanin-containing cells are vaporized with minimal damage to underlying, overlying or adjacent cells. These laser types have a pulse duration too short for optimal effects on larger cellular structures such as hair follicles.
U.S. Pat. No. 5,344,418 to S. Ghaffari discloses an optical system for treatment of skin disorders resulting from blood vessels in the dermis which minimizes damage to epidermal and dermal layers which light must pass through by including a temperature compensation and monitoring system. That system reportedly cools the skin to temperatures as low as 5.degree. C. Specifically, the light, which is from an incoherent source, is passed to a sapphire lens contained in the tip of a conical housing, which includes channels for transporting cooling gas to the sapphire lens. The sapphire lens is placed in contact with the surface of the skin to be treated.
The system disclosed in the Ghaffari patent irradiates the skin and cools the skin during a predetermined time interval in coordination with the delivery of the radiation. The absorption of the radiation by the skin and the change in temperature of the skin is monitored by the system. The operation of the radiation delivery system is controlled to optimize treatment of deep lying vascular lesions. Therefore, the Ghaffari patent discloses selective coagulation enhanced by differential cooling and, as a result, differential heat by the radiation to promote the selective treatment of deep lying vascular lesions. In comparison, the Weissman patent and other patents teaches the selective absorption of radiation to selectively coagulate (i.e., selective coagulation by wavelength absorption) hair follicles and not skin without enhancement by differential cooling.
A disadvantage of the Ghaffari system is that only the skin being irradiated is cooled. The sapphire lens provides focusing of the beam at the point of contact to the skin and the lens requires cooling in its entirety since the light beam is large in comparison to the lens diameter. Therefore, in that system, only treated skin, and not skin adjacent to the treated area, is cooled. U.S. Pat. No. 5,059,192 to Zaias disclosed a method of hair depilation using a ruby red laser. The method disclosed is for treatment of a single or group of hairs while causing minimal damage to the skin. The Zaias patent discloses use of a Q-switched ruby laser with an output at 694 nm, pulse energies from 0.4 to 10 joules/cm.sup.2 and pulse durations of 3040 nanoseconds. This output causes melanosomes adjacent to the base of the hair follicle to rupture due to the rapid high absorption of laser energy, heat production and vaporization of the melanosomes.
More recently, a normal-mode ruby laser has been shown to be effective in hair removal in an article entitled "Damage to Hair Follicles by Normal-Mode Ruby Laser Pulses" by Melanie C. Grossman, M.D., et al., J Amer Acad Dermatology, Vol. 35, No.6, pp. 889-894, 1996. In a controlled study, a beam was used that had a diameter of 6 mm and a pulse length of 270 microseconds, emitting from 30-60 joules/cm.sup.2. Selective photothermolysis was demonstrated, producing prolonged hair growth delay or, in some cases, permanent hair removal. The authors further report that they designed a delivery device which appears to be quite similar to that disclosed in the Ghaffari patent to optimize deep light delivery and limit epidermal injury. Similar to the Ghaffari patent, this included a convergent beam at the skin, a large exposure spot diameter, and a forceful compression of the skin to eliminate blood, deform the dermis and reduce the distance between the surface and the hair. The device was cooled to extract more heat from the dermis on contact.
The device and method of the Grossman article appears to be similar to the subject matter of U.S. Pat. Nos. 5,595,568 and 5,735,844 to Andersen, et al. In the '844 patent, radiation of a selected wavelength is applied through an applicator in contact with the skin for a predetermined time. As in the Ghaffari patent, the applicator is preferably a sapphire lens designed to converge optical radiation applied to the skin (i.e., a lens) and has a means for cooling. Also as in the Ghaffari patent, a sapphire or diamond lens is preferred because of their high thermal conductivity and transparency to visible light. However, the system disclosed in the '844 patent and the Grossman article has the same disadvantages as the Ghaffari patent.
High-peak-power radiation from a pulsed CO.sub.2 laser has been used for predictable vaporization of tissue, either for incision of tissue or for bulk ablation. Furthermore, as an alternative to using a high-energy pulsed CO.sub.2 laser, scanning a continuous-output high-power-density laser beam within a specified area has also been used with the CO.sub.2 laser. This provides a means for controlling localized laser exposure over very short time durations, resulting in predictable vaporization of tissue.
At least three scanners which move a beam of light in a controlled fashion have been commercialized for use with the continuous-wave CO.sub.2 laser including one sold under the trademark Sharplan Lasers Silktouch Scanner, another sold under the trademark Reliant Lasers Accuscan Scanner and another sold under the trademark SAHAR Technologies Scanner. Applications with these scanners and the CO.sub.2 laser include uvulopalatoplasty, skin resurfacing and production of cylindrical puncture sites for hair or skin transplantation. Further, Sharplan commercializes a scanner for use with an alexandrite laser for hair depilation. That system utilizes 2 millisecond pulses with 5-10 millimeter spot sizes over 5.times.5 centimeter areas. That scanner utilizes a ring with a metal perimeter pointer for stable positioning. While there is contact between the scanner and the skin for stable positioning, there is no cooling of the scanner or the skin as part of the assembly design.
U.S. Pat. No. 5,411,502 to E. Zair, et al., shows high-velocity scanning of a high-intensity laser beam over a defined area to be a very effective method of limiting tissue exposure to individual areas within the scanned areas. The net tissue vaporization effects and avoidance of unwanted thermal injury using scanned continuous, low-average-power, laser outputs, have been proven to be comparable to CO.sub.2 lasers that produce pulses of high peak power (500-1,000 watts) for short duration (0.5-4 millisecond) over the same treatment area.
Longer exposures (up to 100 milliseconds) at lower fluences, such as those produced by the scanned continuous output of a diode laser, result in advantageous selective coagulation by wavelength absorption and denaturation of protein within the melanocytes. This selective coagulation is a subset of selective photothermolysis which does not rely upon vaporization and high temperature gaseous effects.
One condition of selective photothermolysis and coagulation enhanced by differential cooling as disclosed in the Ghaffari and Anderson patents and the Grossman article is that the target structure must be heated by the applied laser energy at a rate faster than its rate for cooling. This concept is referred to as thermal relaxation time. The thermal relaxation time of melanosomes has been postulated to range from 250 nanoseconds to one microsecond based on the size of these structures. However, when the total target volume includes the hair follicle and surrounding melanocytes (total diameter 200-300 microns), the estimated thermal relaxation time is 40-100 milliseconds. Importantly, while selective photothermolysis for coagulation is intended to limit thermal injury to adjacent tissue, significant thermal injury to the papilla of the hair follicle adjacent to melanosomes is required to achieve follicle damage and cessation of hair growth. It is important to note that current normal-mode Ruby laser technology has not produced outputs 45 longer than 3 milliseconds. Therefore, a laser that could produce exposures (10-75 msec) to the skin would be expected to have increased efficacy over the current laser technology consistent with other researcher's findings.